class DebugMe {

  /** Prints the value of a geometric series. */
  public static void main( String[] argv ) {

    int      N = 3;
    ListNode geomSeries = createGeomSeries( 1/2, N );
    double   sum = listSum( geomSeries );

    System.out.println( "for N == " + N + ",\n" );
    System.out.println( "    N  | 1 |^i" );
    System.out.println( "   sum |---|   = " + sum );
    System.out.println( "   i=0 | 2 |\n" );
  }

  /**
   * Creates a list built from ListNodes in which each item
   * is one term in the geometric series:
   * 
   *               N
   *              sum (r^i)
   *              i=0
   *
   * @param  r is the base of the geometric series.
   * @param  N maximum exponent of the geometric series, which
   *         is assumed to be non-negative.
   */
  public static ListNode createGeomSeries( double r, int N ) {
    ListNode newTerm = new ListNode(null, null);
    if( N == 0 ) {
      newTerm.item = new Double(1.0);
      newTerm.next = null;
    }
    else {
      newTerm.next = createGeomSeries( r, N - 1 );
      newTerm.item = new Double(((Double) newTerm.next.item).doubleValue() 
				* r);
    }

    return newTerm;
  }


  /**
   *  Computes the sum of terms in a list.  
   *  @param l is linked list represented by ListNodes, 
   *      where each item in the list is assumed to be a Double.
   */
  public static double listSum( ListNode l ) {
    if( l == null )
      return 0.0;

    return ((Double) l.item).doubleValue() + listSum(l.next);
  }
}